1340 Chem. Mater. 2010, 22, 1340–1349 DOI:10.1021/cm902007g
Controlled Design of Size-Tunable Monodisperse Nickel Nanoparticles Sophie Carenco,†,‡ Cedric Boissiere,† Lionel Nicole,† Clement Sanchez,*,† Pascal Le Floch,*,‡ and Nicolas Mezailles*,‡ UPMC Univ Paris 06 - Coll ege de France, Laboratoire de Chimie de la Mati ere Condens ee de Paris, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France, and ‡Laboratoire H et ero el ements et Coordination, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex, France †
Received July 6, 2009. Revised Manuscript Received December 18, 2009
We present here a complete study on a synthesis of nickel nanoparticles involving the reaction of [Ni(acac)2] with oleylamine (OA) and trioctylphosphine (TOP) reactants, whose simultaneous presence and relative amounts are paramount. The role of every reactant in the nucleation and growth of the nanoparticles has been delineated: OA is the reductant and thus controls the nucleation rate, meanwhile TOP provides a tunable surface stabilization through coordination on the Ni(0) surface. This result leads us to a design synthesis providing tailored monodispersed nanoparticles in a wide range (2-30 nm), which allows self-consistent studies of size-induced changes in catalytic and magnetic properties. Additionally, the growth mechanism is demonstrated to include an aggregation step which thus correlates with the polycrystalline feature of the nanoparticles obtained through this process. Moreover, the critical influence of the phosphine in this system was demonstrated a) for the outcome of the ripening mechanisms: defocusing effect and/or reshaping of the particles and b) for the surface properties: binding of the phosphine to the surface and its behavior toward oxidation was investigated by FTIR. Preliminary SQUID measurements show the impact of crystallites size on the magnetic properties. 1. Introduction Size, shape, and surface state of metallic nanoparticles (NPs) are of paramount importance for a whole range of applications based on catalytic, optical, or magnetic properties.1,2 Among all synthetic pathways, only a few have been understood in great detail after extensive studies, namely the Au(0) and Ag(0) systems.3 The development of easy and well-defined syntheses giving access to a variety of size range, from clusters to bulk-like particles, becomes critical for precise studies of the size influence. Indeed, fine parameters such as the percentage of ligand coverage or a partial oxidation on the surface of the particles are not easily measured but strongly modulate catalytic activities or magnetic behavior. Among those parameters, the nature and abundance of surfactants, ligands, or stabilizers at the surface of the particles are critical for the outcome of the synthesis and consequently on the existence of any property of the particles.4-7 Many models have been elaborated for the *Corresponding author. Fax: (þ33) 1 44 27 15 04. Tel: (þ33) 1 44 27 15 02. E-mail:
[email protected] (C.S.). Fax: (þ33) 1 69 33 44 49. Tel: (þ33) 1 69 33 44 02. E-mail:
[email protected] (P.L.F.). E-mail:
[email protected] (N.M.).
(1) Hyeon, T. Chem. Commun. 2003, 927. Sun, S.; Murray, C. B.; Weller, D.; Folks, L.; Moser, A. Science 2000, 287, 1989. (2) Han, J.; Liu, Y.; Guo, R. J. Am. Chem. Soc. 2009, 131, 2060. Lee, I.; Delbecq, F.; Morales, R.; Albiter, M. A.; Zaera, F. Nat. Mater. 2009, 2, 132. (3) Grzelczak, M.; Perez-Juste, J.; Mulvaney, P.; Liz-Marzan, L. M. Chem. Soc. Rev. 2008, 37(9), 1783. (4) Yu, W. W.; Wang, Y. A.; Peng, X. Chem. Mater. 2003, 15, 4300. (5) Yin, Y.; Alivisatos, A. P. Nature 2005, 437, 664. (6) Garnweitner, G.; Niederberger, M. J. Mater. Chem. 2008, 18, 1171. (7) Zhiqiang, Y; Klabunde, K. J. J. Organomet. Chem. 2009, 694, 1016.
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nucleation and growth of the nanoparticles, highlighting the necessity to understand the role of every component in the synthesis.8-10 Monodispersed nickel nanoparticles display attractive properties in relation with their size. As a catalytic material, their activity has mainly been established in heterogeneous processes, where the surface of the metal is directly accessible.11 An application is the homogeneous Suzuki crosscoupling recently reported by Hyeon et al. highlights the influence of the stabilizing ligand on the activity and selectivity of the catalyst.19 Several synthetic approaches toward nickel nanoparticles have been developed, such as the polyol synthesis,12,13 electrochemical reductions,14 sol-gel (8) Park, J.; Joo, J.; Kwon, S. G.; Jang, Y.; Hyeon, T. Angew. Chem., Int. Ed. 2007, 46, 4630. Casula, M. F.; Jun, Y. W.; Zaziski, D. J.; Chan, E. M.; Corrias, A.; Alivisatos, A. P. J. Am. Chem. Soc. 2006, 128, 1675. (9) Shevchenko, E. V.; Talapin, D. V.; Schnablegger, H.; Kornowski, € Svedlindh, P.; Haase, M.; Weller, H. J. Am. Chem. A.; Festin, O.; Soc. 2003, 125, 9090. Cushing, B. L.; Kolesnichenko, V. L.; O'Connor, C. J. Chem. Rev. 2004, 104, 3893. (10) Polleux, J.; Pinna, N.; Antonietti, M.; Niederberger, M. Adv. Mater. 2004, 16(5), 436. (11) Xu, B. Q.; Wei, J. M.; Yu, Y. T.; Li, J. L.; Zhu, Q. M. Top. Catal. 2003, 22, 77. Haag, S.; Burgard, M.; Ernst, B. J. Catal. 2007, 252, 190. (12) Murray, C. B.; Sun, S.; Doyle, H.; Betley, T. MRS Bull. 2001, 26, 985. (13) Hinotsu, T.; Jeyadevan, B.; Chinnasamy, C. N.; Shinoda, K.; Tohji, K. J. Appl. Phys. 2000, 95, 7477. Tzitzios, V.; Basina, G.; Gjoka, M.; Alexandrakis, V.; Georgakilas, V.; Niarchos, D.; Boukos, N.; Petridis, D. Nanotechnology 2006, 17, 3750. (14) Sun, Y. P.; Rollins, H. W.; Guduru, R. Chem. Mater. 1999, 11, 7. Chen, D. H.; Hsieh, C. H. J. Mater. Chem. 2002, 12, 2412. Jeon, Y. T.; Moon, J. Y.; Lee, G. H.; Park, J.; Chang, Y. J. Phys. Chem. B 2006, 110, 1187. Zach, M. P.; Penner, R. M. Adv. Mater. 2000, 12, 878.
Published on Web 01/29/2010
r 2010 American Chemical Society
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technique,15 microwave heating,16 seeding techniques,17 or reduction of an organometallic precursor,18-21 each of them leading to a specific size range. In this last category, a Ni(II) precursor is reduced either at low temperature with a strong reductant such as sodium tetrahydridoborate22 or at high temperature by a mixture containing amine and/or carboxylic acid.23 In the first case, the reductant is clearly identified, but the nucleation is swift thus hard to control. In the second case, the synthesis goes through complex mechanisms due to the apparition of intermediates (such as in situ formation of carboxylate complexes and acid-base equilibrium), which makes a tailored synthesis hardly reachable. An additional approach consists of decomposing a Ni(0) precursor, such as bis(cyclooctadiene)nickel, in the presence of a ligand, which allows for a good shape control.24-26 The sole drawback of this method is the high reactivity of the airsensitive Ni(0) precursors. However, it appears that most of these synthetic methods cannot give access to monodisperse particles with a broad range of size without critically modifying the nature of the stabilizing ligand and the reducer: this renders it difficult to both the understanding of the synthesis and the direct comparison of the size influence on a particular property. Moreover, the ripening mechanisms have rarely been discussed even though they are relevant for the final properties of the particles. Here, we present a systematic investigation of the synthesis of Ni(0) nanoparticles by the thermal reduction of a Ni(II) precursor, using a binary ligand system consisting of an amine (oleyamine, OA) and a phosphine (trioctylphosphine, TOP). Although similar synthesis was already described in literature, the specific contribution of OA and TOP on nucleation and growth of Ni NPs were scarcely investigated. Our main goal in this study is to precisely delineate the role of each component in the reaction mixture. This understanding allowed us to define (15) Chatterjee, A.; Chakravorty, D. Appl. Phys. Lett. 1992, 60, 138. Yang, J.; Feng, B.; Liu, Y.; Zhang, Y.; Yang, L.; Wanga, Y.; Wei, M.; Lang, J.; Wang, D.; Liu, X. Appl. Surf. Sci. 2008, 254, 7155. (16) Parada, C.; Moran, E. Chem. Mater. 2006, 18, 2719. (17) Grzelczak, M.; Perez-Juste, J.; Rodriguez-Gonzalez, B.; Spasova, M.; Barsukov, I.; Farle, M.; Liz-Marzan, L. M. Chem. Mater. 2008, 20, 5399. (18) Wang, H.; Jiao, X.; Chen, D. J. Phys. Chem. C 2008, 112, 18793. Chen, Y.; Luo, X.; Yue, G. H.; Luo, X.; Peng, D. L. Mater. Chem. Phys. 2009, 113, 412. Green, M.; O'Brien, P. Chem. Commun. 2001, 1912. (19) Park, J.; Kang, E.; Son, S.; Park, H.; Lee, M.; Kim, J.; Kim, K.; Noh, H.; Park, J.; Bae, C.; Park, J.; Hyeon, T. Adv. Mater. 2005, 17, 429. (20) Chen, Y.; Peng, D.; Lin, D.; Luo, X. Nanotechnology 2007, 18, 505703. Zhang, H. T.; Wu, G.; Chen, X. H.; Qiu, X. G. Mater. Res. Bull. 2006, 41, 495. Goto, Y.; Taniguchi, K.; Omata, T.; Otsuka-YaoMatsuo, S.; Ohashi, N.; Ueda, S.; Yoshikawa, H.; Yamashita, Y.; Oohashi, H.; Kobayashi, K. Chem. Mater. 2008, 20, 4156. (21) Han, M.; Liu, Q.; He, J. H.; Song, Y.; Xu, Z.; Zhu, J. M. Adv. Mater. 2007, 19, 1096. (22) Hou, Y.; Gao, S. J. Mater. Chem. 2003, 13, 1510. (23) Han, M.; Liu, Q.; He, J.; Song, Y.; Xu, Z.; Zhu, J. Adv. Mater. 2007, 19, 1096. (24) Bradley, J.; Tesche, B.; Busser, W.; Maase, M.; Reetz, M. J. Am. Chem. Soc. 2000, 122, 4631. (25) Ely, T. O.; Amiens, C.; Chaudret, B. Chem. Mater. 1999, 11, 526. Cordente, N.; Respaud, M.; Senocq, F.; Casanove, M. J.; Amiens, C.; Chaudret, B. Nano Lett. 2001, 1, 565. (26) Carenco, S.; Resa, I.; Le Goff, X.; Le Floch, P.; Mezailles, N. Chem. Commun. 2008, 2568.
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Figure 1. Left: nickel NPs synthesized with 10 equiv of OA (50-80 nm). Right: nickel NPs synthesized with 10 equiv of TOP (2 nm).
for the first time conditions for the rational synthesis of monodispersed Ni(0) particles with tailored sizes: ca. from 2 to 30 nm. In the present paper, we investigate the growth mechanism and evidence for the first time a crucial implication of aggregation in this process. Additionally, we were able to characterize two mechanisms of ripening affecting strongly the monodispersity and the morphology of the nanoparticles, for which we propose a rationalization based on the phosphine stoichiometry. As a first step toward application in the field of catalysis, the shell of ligands and its behavior at air contact is analyzed using IR spectroscopy. Additionally, we report preliminary magnetic characterization by SQUID, as an initial study supporting our designed pathway toward tailored monodispersed nickel nanoparticles. 2. Results and Discussion In a typical synthesis, [Ni(acac)2] was dissolved in a solution containing oleylamine (x equiv) and/or trioctylphosphine (y equiv). In order to make pertinent comparisons between the various experiments, the concentration of the Ni species had to be constant. This was achieved by the addition of appropriate amounts of 1-octadecene (ODE). The reaction mixture was then heated at 220 °C for 2 h, yielding a black solution of nanoparticles subsequently isolated by centrifugation and redispersed in hexanes.27 The particles were systematically analyzed by XRD and TEM. 2.1. Reduction of the Ni(II) Precursor by TOP. In the first series of experiments, the effect of TOP was studied. Quite surprisingly, even at 220 °C, TOP was shown to be a poor reducing agent for the nickel complex [Ni(acac)2]. Indeed, when the synthesis was conducted with 10 equiv of TOP (without oleylamine and without ODE), the complete reduction was far from being achieved within 2 h, as attested by the green-black color of the mixture (presence of starting [Ni(acac)2]). Only about 30% of the expected amount of nanoparticles was recovered upon precipitation. Nevertheless, the isolated particles were readily dispersed in nonpolar solvents such as hexanes. The TEM analysis (Figure 1, right-hand side) of these (27) Note that it is well-known in the literature that the TOP ligand does not decompose at this temperature to form nickel phosphide particles but above 330 °C.
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Figure 2. Nickel NPs synthesized with 10 OA and 0.8 TOP (9 nm, σ
